Biotechnology giant Biogen Inc. has drawn takeover interest from drug companies including Merck & Co. and Allergan PLC, raising the possibility of another huge deal in the health-care industry.

Merck and Allergan have each sounded out Biogen on the possibility of a takeover, people familiar with the matter said. The communications were informal and preliminary, and they may not result in a deal—in part because Biogen may not be interested, they added.